Marine pipeline installation system and methods

ABSTRACT

A method for installing an accessory onto a pipeline to be laid on the seabed, includes launching the pipeline from a first position of a tower in which the tower is at an angle α with respect to the vertical; stopping the launch of the pipeline, and hanging off the launched pipeline in a hang off module; positioning an accessory in a tower firing line; attaching the accessory to the launched pipeline in the hang off module and to at least one A&amp;R cable; suspending the accessory and the launched pipeline from an A&amp;R system; disengaging the hang off module from the launched pipeline; pivoting the pipeline launch tower to an accessory launch position in which the tower is at an angle γ that differs substantially from angle α, such that a pipeline launch trajectory is created which is large enough to launch the accessory and the launched pipeline with the A&amp;R system.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of co-pending U.S. patent applicationSer. No. 12/990,052 filed on Jan. 7, 2011, which is the National Phaseof PCT/NL2008/000117 filed on Apr. 29, 2008, all of which are herebyexpressly incorporated by reference into the present application.

A first aspect of the invention relates to a method for installing anaccessory onto a pipeline to be laid on the seabed, wherein use is madeof a marine pipeline installation system for laying an offshore pipelinecomprising:

-   -   a vessel,    -   a pipeline launch tower having pipe laying equipment defining a        tower firing line, which tower is mounted pivotably on said        vessel and which is adapted for launching the pipeline along the        tower firing line into the sea in a first position of the tower        in which the tower is at an angle α with respect to the        vertical,    -   a hang off module supported in the lower part of the firing line        for clamping and supporting the weight of previously launched        pipeline,    -   an abandonment and recovery (A&R) system comprising at least one        A&R cable and a sheave arrangement with one or more sheaves        provided at an upper position in the firing line,    -   an accessory handling device for positioning the accessory        between the hang off module and the abandonment and recovery        sheave arrangement in the firing line.

Such marine pipeline installation systems are well known in the art,preferably for laying an offshore pipeline and/or installing a subseariser. Such a system comprises a vessel having a bow and a stern, whichvessel may be suitable to carry out the reel lay method, laying rigid orflexible pipelines, but may also be suitable to carry out the J-laymethod.

The system further comprises a pipeline launch tower comprising pipelaying equipment defining a tower firing line, which tower is mountedpivotably on said vessel. The tower is adapted for launching thepipeline in the firing line in the direction of the seabed in a firstposition of the tower in which the tower is at an angle α with respectto the vertical. The pipe laying equipment may comprise tensioners, e.g.when the tower is used for reel laying operations, and may furthermoreinclude welding stations and line-up tools, e.g. when the tower is usedfor J-lay operations. Furthermore, the pipe laying equipment may includeclamps such as a hang off module clamp provided in a hang off module.

Such a tower is often placed adjacent or over a moonpool of the vessel,or at another suitable location, e.g. at the stern of the vessel. Ingeneral the term tower here refers to a raised structure on the vessel,and may e.g. be designed as a reel lay ramp. Alternatively or inaddition, the tower may be formed by an A-frame.

A hang off module is supported in the lower part of the firing line tosupport a previously launched pipeline. Such a hang off module may beallowed to engage with the launched pipeline, e.g. by clamping. In apossible embodiment, the hang off module is supported by the vessel andcomprises associated hang off module pivoting means to pivot the hangoff module together with or independent of the tower. In an alternativeembodiment, the hang off module is supported by the pipeline launchtower and is pivotable together with the tower.

The pipeline launch tower supports an abandonment and recovery (A&R)system comprising at least one A&R cable and a sheave arrangement,comprising one or more A&R sheaves. Such A&R system can be used forlowering the launched pipeline, accessories, or launched pipelineprovided with an accessory. Examples of such accessories are pipelineend terminals (PLET's) and connectors. Preferably, the A&R sheavearrangement is provided at an upper position of the pipeline launchtower, such that the accessory is positionable below the sheavearrangement.

Accessories may be stored on the deck area or alternatively on a barge.Such accessories are positioned in the firing line between the hang offmodule and the abandonment and recovery sheave arrangement by anaccessory handling device. The accessory may be delivered to theaccessory handling device by a crane, such as an offshore mast crane ora knuckle boom crane, or via an A&R cable in the A&R system. Possiblyalso the accessory handling device is skiddable into the firing line.

The first aspect of present invention aims to provide an improved methodfor installing accessories onto a pipeline to be laid on the seabed, orat least an alternative method.

The method according to the first aspect of the invention comprises thefollowing steps:

-   -   launching the pipeline from the first position of the tower in        which the tower is at an angle α with respect to the vertical,        in a pipeline launch trajectory corresponding to the tower        firing line into the sea,    -   stopping the launch of pipeline, and hanging off the launched        pipeline in the hang off module,    -   positioning the accessory in the tower firing line,    -   attaching the accessory to the launched pipeline in the hang off        module and to the at least one A&R cable,    -   suspending the accessory and the launched pipeline from the A&R        system,    -   disengaging the hang off module from the launched pipeline,    -   pivoting the pipeline launch tower to an accessory launch        position in which the tower is at an angle γ with respect to the        vertical, which angle γ differs substantially from angle α, such        that a pipeline launch trajectory is created which is large        enough to launch the accessory and the launched pipeline with        the A&R system,    -   lowering the accessory with the launched pipeline by the A&R        system.

This way, the accessory and the launched pipeline suspending from theA&R system are at a distance from the tower. The line in which theaccessory and the launched pipeline suspend from the A&R system may bereferred to as the A&R line. Rotating the pipeline launch tower awayfrom the pipeline launch trajectory in which an accessory is installedonto a pipeline facilitates the lowering of accessories. The firing lineof the tower is at an angle with the pipeline launch trajectory,possibly angle (γ-α), which angle preferably exceeds 7° and morepreferably exceeds 15°, such that a pipeline launch trajectory iscreated which is large enough to launch the accessory and the launchedpipeline with the A&R system. This is in particular beneficial when thespace available in the tower firing line is limited, and largeaccessories are to be handled. The more the pipeline launch tower ispivoted, the more the A&R line is remote from the tower firing line.Another advantage may be that is not necessary to remove the pipelayingequipment from the firing line, e.g. by displacement or bydisengagement. In a preferred embodiment, relatively small accessoriesmay be launched in the firing line of the tower in the pipeline launchtrajectory, while the tower is pivoted to the accessory launch positionto launch relatively large accessories.

In a preferred embodiment, the A&R line extends well beyond the stern orthe bow of the vessel, or beyond the gangways. Large, oversizedaccessories such as PLETs, which e.g. do not fit in between the legs ofthe pipeline launch tower or ramp may thus be installed at a remotelaunch trajectory: the A&R line.

Preferably, when the accessory comprises a pipe end portion, the methodaccording to the first aspect of the invention further comprises thesteps of:

-   -   launching the accessory and the launched pipeline by the A&R        cable until the pipe end portion is at the same height level as        the position of the hang off module,    -   pivoting the pipeline launch tower from the accessory launch        position in which the tower is at an angle γ with respect to the        vertical back to the first position in which the tower is at an        angle α with respect to the vertical, such that the pipeline        launch trajectory again coincides with the firing line of the        tower,    -   engaging the pipe end portion to the hang off module,    -   detaching the A&R cable from the accessory.

In a preferred embodiment according to the first aspect of the inventionthe tower includes in the first position an acute angle α with theintended direction of movement of the vessel during pipelaying, whereinthe tower is pivoted to a less acute angle γ or to a more acute angle γin the accessory launch position of the tower, such that the firing lineof the tower is at an angle, preferably angle (γ-α) with the pipelinelaunch trajectory, such that a pipeline launch trajectory is createdwhich is large enough to launch the accessory and the launched pipelinewith the A&R system.

Alternatively, the tower includes in the first position an obtuse angleα with the intended direction of movement of the vessel duringpipelaying, and wherein the tower is pivoted to a less obtuse angle γ orto a more obtuse angle γ in the accessory launch position of the tower,such that the firing line of the tower is at an angle (γ-α) with thepipeline launch trajectory.

In yet an alternative embodiment, the tower includes in the firstposition an acute angle α with the intended direction of movement of thevessel during pipelaying, and wherein the tower is pivoted to an obtuseangle γ in the accessory launch position of the tower.

Analogously, in yet an alternative embodiment, the tower includes in thefirst position an obtuse angle α with the intended direction of movementof the vessel during pipelaying, and wherein the tower is pivoted to anacute angle γ in the accessory launch position of the tower.

A second aspect of the invention relates to a marine pipelineinstallation system for laying an offshore pipeline, preferably forlaying an offshore pipeline and/or installing a subsea riser. Such asystem comprises a vessel, which vessel may be suitable to carry out thereel lay method, laying rigid or flexible pipelines, but may also besuitable to carry out the J-lay method.

The system further comprises a pipeline launch tower comprising pipelaying equipment defining a tower firing line, which tower is mountedpivotably about a pivot axis on said vessel. The tower is adapted forlaunching the pipeline in the firing line in the direction of the seabedin a first position of the tower in which the tower is at an angle αwith respect to the vertical. The pipe laying equipment may comprisetensioners, e.g. when the tower is used for reel laying operations, andmay furthermore include welding stations and line-up tools, e.g. whenthe tower is used for J-lay operations. Furthermore, the pipe layingequipment may include clamps such as a hang off module clamp provided ina hang off module.

Such a tower is often placed adjacent or over a moonpool of the vessel,or at another suitable location, e.g. at the stern of the vessel. Ingeneral the term tower here refers to a raised structure on the vessel,and may e.g. be designed as a reel lay ramp. Alternatively or inaddition, the tower may be formed by an A-frame.

The marine pipeline installation system according to the second aspectof the invention further comprises a workstation comprising a workingplatform supported by a support frame and accessible to personnel toperform inspection operations etc., which workstation is supported inthe lower part of the pipeline launch tower. The working station mayfurther comprise welding equipment for welding pipe sections to eachother or to accessories.

Furthermore, the marine pipeline installation system comprises a hangoff module supported by the support frame in the lower part of the towerfiring line for clamping and supporting the weight of the previouslylaunched pipeline.

The second aspect of the present invention aims to provide an improvedmarine pipelaying system, or at least an alternative system.

According to the second aspect of the invention the support frame isskiddable along a support frame guide provided in the lower part of thepipeline launch tower, which support frame guide is substantiallyperpendicular to the tower pivot axis and substantially perpendicular tothe tower firing line, such that the working platform and the hang offmodule are skiddable into and out of the tower firing line.

Thus, the second aspect of the invention provides a system allowing aworking platform to be positioned into the tower firing line, enablingalmost or full 360° inspection of a pipeline in the tower firing linewhen the working platform is positioned into the tower firing line. Theworking platform may comprise a slot at the tower firing line side ofthe working platform to receive a pipeline in the tower firing line whenthe working platform is positioned in the tower firing line. This makesit easier for personnel to get near the pipeline from differentdirections.

The ability to position the working platform out of the tower firingline is advantageous when for instance an accessory or thickening in thepipeline has to pass the working station. The working platform is thenpositioned out of the tower firing line, such that the working platformis not interfering with the accessory or thickening.

Preferably, a platform pivot axis parallel to the tower pivot axis isprovided between the support frame and the working platform, such thatthe working platform can gimbal maintaining a horizontal positionindependent of the position of the tower. The pipeline launch tower ismounted pivotably about a pivot axis and can take many positions withrespect to the vessel, which can also be changed during normaloperations. To move naturally across the working platform duringinspection operations etc., the working platform needs to be placedsubstantially horizontal independent of the position of the tower. Theplatform pivot axis allows this independent movement. The relativemovement of the working platform with respect to the tower can beachieved by gimbal means, comprising preferably a cylinder or a gearwheel and motor. Other gimbal means to pivot the working platformrelatively with respect to the tower are also conceivable.

In an embodiment, the working platform comprises two platform portionsbetween which a swinging axis parallel to the tower pivot axis isprovided, such that the platform portion closest to the tower firingline can be swung back so as to clear the area around the tower firingline. The advantage is that with a relatively large working platform andrelatively little movement of the working platform along the supportframe guide, enough area is cleared around the tower firing line,because the platform portion closest to the tower firing line can beswung back.

The swinging axis preferably coincides with the platform pivot axis, butthe swinging axis may also be located between the platform pivot axisand the free end of the platform portion closest to the tower firingline.

If the platform portion closest to the tower firing line comprises aslot which extends from the free end of the working platform to theswinging axis, the platform portion is divided into two parts which maybe swung back independent from each other.

In an embodiment, the marine pipeline installation system furthercomprises an abandonment and recovery (A&R) system comprising at leastone A&R cable and a sheave arrangement with one or more sheavessupported by the pipeline launch tower.

Preferably, the support frame further supports one or more of the A&Rsheaves, such that the one or more sheaves supported by the supportframe are skiddable into and out of the tower firing line. The sheavessupported by the support frame can guide the A&R cable, which isespecially advantageous when the tower is in an inclined position.

The mobility of the support frame allows to adapt the position of theone or more sheaves supported by the support frame, such that theposition of the one or more sheaves is adaptable to the position of theat least one A&R cable to be guided by the one or more sheaves. Thus,the A&R cable can pass the sheaves supported by the support frame at twosides, dependent on the angle of the tower.

The third aspect of the invention relates to a marine pipelineinstallation system for laying an offshore pipeline, preferably forlaying an offshore pipeline and/or installing a subsea riser. Such asystem comprises a vessel, which vessel may be suitable to carry out thereel lay method, laying rigid or flexible pipelines, but may also besuitable to carry out the J-lay method.

The system further comprises a pipeline launch tower comprising pipelaying equipment defining a tower firing line, which tower is mountedpivotably about a pivot axis on said vessel. The tower is adapted forlaunching the pipeline in the tower firing line in the direction of theseabed in a first position of the tower in which the tower is at anangle α with respect to the vertical. The pipe laying equipment maycomprise tensioners, e.g. when the tower is used for reel layingoperations, and may furthermore include welding stations and line-uptools, e.g. when the tower is used for J-lay operations. Furthermore,the pipe laying equipment may include clamps such as a hang off moduleclamp provided in a hang off module.

Such a tower is often placed adjacent or over a moonpool of the vessel,or at another suitable location, e.g. at the stern of the vessel. Ingeneral the term tower here refers to a raised structure on the vessel,and may e.g. be designed as a reel lay ramp. Alternatively or inaddition, the tower may be formed by an A-frame.

Furthermore, the system comprises an abandonment and recovery (A&R)system comprising at least one A&R cable and a sheave arrangement withone or more sheaves supported by the pipeline launch tower. Mostconventional marine pipeline installation systems provide the entire A&Rsheave arrangement at an upper position of the pipeline launch tower. Adisadvantage sheaves only provided at an upper position of the pipelinelaunch tower is that this possibly causes A&R cables to scrap along theramp or edges of the vessel, or, when the pipeline launch trajectorypasses a moonpool, along the edges of the moonpool, even with small offlead and side lead angles.

Furthermore, the marine pipeline installation system comprises a hangoff module supported by the support frame in the lower part of the towerfiring line for clamping and supporting the weight of the previouslylaunched pipeline.

The third aspect of the present invention aims to provide an improvedmarine pipelaying system, or at least an alternative system.

According to the third aspect of the invention the hang off module andone or more of the sheaves having a sheave pivot axis substantiallyparallel to the tower pivot axis are supported by a support frame, whichis skiddable along a support frame guide provided in a lower part of thepipeline launch tower, which guide is substantially perpendicular to thetower pivot axis and substantially perpendicular to the tower firingline, such that the one or more sheaves and the hang off modulesupported by the support frame are skiddable into and out of the towerfiring line.

The provision of one or more sheaves provided at the lower part of thetower guiding the cables from the upper A&R sheaves along the pipelinelaunch tower allows restraining of the A&R wire at a lower position thanat an upper position of the pipeline launch tower, increasing vesselstability significantly. Preferably, the distance between the sheavesprovided at the upper part of the tower and the lower part of the toweris such that accessories may be positioned between the sheaves.

The advantage of supporting one or more sheaves by the support frame isthat the sheaves can be moved into and out of the tower firing line,enabling the passage of an accessory or thickening in the pipeline.

Because the pipeline launch tower can pivot to both positive andnegative angles with respect to the vertical, it is advantageous to beable to guide the at least one A&R cable for both angles of the tower.This is possible according to a preferred embodiment of the third aspectof the invention, wherein at least one of the sheaves supported by thesupport frame is adapted to guide the at least one A&R cable at oppositesides of the sheave, and the support frame is at least skiddable betweena position in which the at least one A&R cable is guided by a first sideof the sheave and another position in which the at least one A&R cableis guided by an opposite side of the sheave.

In an embodiment, at least one of the sheaves supported by the supportframe is movable in a direction substantially parallel to the towerpivot axis. In this way, the at least one movable sheave can be lined upwith an A&R cable, but can also be deliberately misaligned to be able topass the A&R cable, get lined up again, and then guide the A&R cable atthe other side of the A&R cable.

In another embodiment, two sheaves are supported by the support frame,at least one of which is moveable in a direction substantially parallelto the tower pivot axis, such that the A&R system is adjustable from asingle fall system in which the moveable sheave is positioned adjacent asingle A&R cable to guide this single A&R cable, to a double fall systemin which the two sheaves are positioned adjacent two A&R cables to guidethese two A&R cables.

The support frame may further support a working platform accessible topersonnel to perform inspection operations etc., such that the workingplatform is skiddable into and out of the tower firing line.

The ability to position the working platform out of the tower firingline is advantageous when for instance an accessory or thickening in thepipeline has to pass the working station. The working platform is thenpositioned out of the tower firing line, such that the working platformis not interfering with the accessory or thickening.

Preferably, a platform pivot axis parallel to the tower pivot axis isprovided between the support frame and the working platform, such thatthe working platform can gimbal maintaining a horizontal positionindependent of the position of the tower. The pipeline launch tower ismounted pivotably about a pivot axis and can take many positions withrespect to the vessel, which can also be changed during normaloperations. To move naturally across the working platform duringinspection operations etc., the working platform needs to be placedsubstantially horizontal independent of the position of the tower. Theplatform pivot axis allows this independent movement. The relativemovement of the working platform with respect to the tower can beachieved by gimbal means, comprising preferably a cylinder or a gearwheel and motor. Other gimbal means to pivot the working platformrelatively with respect to the tower are also conceivable.

In an embodiment, the working platform comprises two platform portionsbetween which a swinging axis parallel to the tower pivot axis isprovided, such that the platform portion closest to the tower firingline can be swung back so as to clear the area around the tower firingline. The advantage is that with a relatively large working platform andrelatively little movement of the working platform along the supportframe guide, enough area is cleared around the tower firing line,because the platform portion closest to the tower firing line can beswung back.

The swinging axis preferably coincides with the platform pivot axis, butthe swinging axis may also be located between the platform pivot axisand the free end of the platform portion closest to the tower firingline.

If the platform portion closest to the tower firing line comprises aslot which extends from the free end of the working platform to theswinging axis, the platform portion is divided into two parts which maybe swung back independent from each other.

A fourth aspect of the present invention relates to the field of marinepipeline installation, in particular for laying an offshore pipelineand/or installing a subsea riser, said system at least being adapted tocarry out the reel lay method. The system according to the fourth aspectof the present invention may be suitable for laying flexible pipelinesbut also for laying rigid pipelines with the reel lay method. Inparticular is the system according to the fourth aspect of the presentinvention suitable for laying pipelines with a steel overall diameterranging from 5-100 cm, preferably 10-50 cm and a maximum plastic bendingmoment of 5000 kNm, preferably 3000 kNm.

From the prior art reel lay vessels are known for laying a pipeline onthe seabed according to the reel lay method. These vessels commonly areequipped with one or more storage reels for storage of pipeline to beinstalled. Such reels may store several hundreds of tons of pipeline,e.g. 3500 metric tons.

The vessels also are equipped with a pipeline launch tower comprisingpipe laying equipment defining a firing line, which tower is mountedpivotably on said vessel and which is adapted for launching the pipelinefrom a storage reel via the firing line in the direction of the seabedin a first position in which the tower is at an angle α with respect tothe vertical. The actual trajectory of the pipeline is also referred toas the pipeline launch trajectory, which thus during launch coincideswith the firing line.

The angle α may be such that the tower includes an acute angle with thedeck of the vessel or alternatively an obtuse angle. The tower may bepivoted to include an acute or obtuse angle with the direction ofmovement of the vessel during pipelaying. The tower may be pivoted alongthe longitudinal axis of the vessel or alternatively be pivotedperpendicular to the longitudinal axis of the vessel as is e.g. the caseon the Pertinacia.

Such a tower may be placed adjacent or over a moonpool of the vessel, orat any other suitable location, e.g. at the stern of the vessel, or atthe bow, or at one of the side parts. In general the term tower hererefers to a raised structure on the vessel, and may e.g. be designed asa reel lay ramp. Alternatively or in addition, the tower may be formedby an A-frame.

The pipe laying equipment for such a marine pipeline installation systemcomprises a pipeline guide provided at an elevated position on saidtower providing a curved path for guiding said pipeline from the reel inthe firing line of said tower. Known pipeline guides include a largediameter pipeline guide wheel or a semi-circular guide structure, e.g.provided with rollers or chains. Such pipeline guide is sometimesreferred to as an aligner.

In known reel lay pipelaying systems the pipe laying equipment furthercomprises one or more pipeline tensioners, commonly two but versionswith one or three are also known, which are supported by the tower atdifferent heights below the pipeline guide.

In a common design each pipeline tensioner has a tensioner frame andmultiple tracks (also called caterpillars), often three or four tracks,supported by said tensioner frame. The tracks are adapted for engagingthe pipeline and supporting at least part of the weight of the launchedpipeline. In practice a single tensioner can be designed to support apipeline weight of more than 50 tons, and tensioner capacities of morethan 100 tons, even up to 450 tons are also not uncommon.

The tracks are mounted in said tensioner frame in a movable manner inorder to allow for adjustment of the gap between the tracks toaccommodate various pipeline diameters.

The present invention aims to provide an improved marine pipelayingsystem, or at least an alternative system.

The present invention provides according to a fourth aspect thereof asystem for marine pipeline installation on which the pipeline launchtower is pivotable to a second position in which the tower is at anangle β with respect to the vertical, which angle β is opposite to angleα, in which second position the pipeline can also be launched from astorage reel into the sea.

Thus, according to the fourth aspect of the invention in the firstposition of the tower the tower may be inclined at a range of anglesbelow vertical, allowing the launch of pipeline in many positions of thetower. The inclination α may be in the range between 0 and 70°, morepreferably between 0 and 15°, whereby an inclination of 0° correspondsto a vertical orientation of the pipeline launch tower. In the secondposition the tower may be inclined at a range of angles below vertical,opposite to the first position.

Thus, where a tower positioned at an edge of the vessel (the bow, thestern or a side of the vessel) is pivoted to include an acute angle withthe deck in the first position, in the second position the towerincludes an obtuse angle with the deck. Analogously, the tower mayinclude an obtuse angle with the deck in the first position and an acuteangle in the second position. In a preferred embodiment, the pipelinelaunch tower is positioned at the stern of the vessel and is pivotablebetween a position in which the tower is positioned inclined withrespect to the bow with 65° to a second position in which the tower isleaning backwards and extending over the stern with 15°.

In a preferred embodiment, the tower is pivoted in the first position toinclude an acute angle with the forward direction of movement of thevessel during pipelaying, and in the second position to include anobtuse angle with the forward direction of movement of the vessel duringpipelaying.

The invention thus allows pipelaying during a forward movement of thevessel and during a rearward movement of the vessel. This may inparticular be advantageous when little space is available, e.g. close toexisting offshore installations. It may also prevent unnecessarymanoeuvring of the vessel. In pipe laying operations usually the speedof the reel is set by the operator, and the tensioners follow the speedof the reel to maintain a constant back tension. This is controlled by acontrol system. Backward laying operations allow the vessel to sailbackwards to a platform while laying pipe and when it arrives at theplatform the pipe can be handed over to the platform relatively easy.

A hang off module may be supported below the tensioners in the firingline to support a previously launched pipeline. Such a hang off modulemay be allowed to engage with the launched pipeline, preferably byclamping. In a possible embodiment, the hang off module is supported bythe vessel and comprises associated hang off module pivoting means topivot the hang off module together with or independent from the tower.In an alternative embodiment, the hang off module is supported by thepipeline launch tower and is pivotable together with the tower.

In a particular embodiment the tensioner frame is designed ‘oversized’with respect to regular pipeline diameters, so that the gap between thetracks can be increased to a large size which allows for the passage ofan accessory fitted on (the end of) or in the pipeline, e.g. a connectoron the end of or in a flexible pipeline. Such connectors are bulky andhave a diameter substantially greater than the pipeline diameter, e.g.having a diameter of more than 1 meter for connectors in flexibleoffshore pipeline. Thus, the tensioners may allow the passage of theconnection devices while tension is maintained. When the connectingdevice has passed the tensioners, the hang off module is activated. Theend connections, possibly including a few meters of pipe that has to beremoved due to straightening inaccuracies, caused by the pipeconnection, are removed and the pipe ends are welded together.

It is common for pipeline launch towers to further support anabandonment and recovery (A&R) system comprising one or more A&R cablesand a sheave arrangement, comprising one or more A&R sheaves. Such A&Rsheave arrangement can be used for lowering the launched pipeline,accessories, or launched pipeline provided with an accessory. Examplesof such accessories are pipeline end terminals (PLET's) and connectors.Preferably, the A&R sheave arrangement is provided at an upper positionof the pipeline launch tower, such that the accessory is positionablebelow the sheave arrangement.

A preferred embodiment of the pipeline launch tower used for layingrigid pipes further carries a radius controller and/or one or morestraightener tracks for conditioning the rigid pipe at a positionupstream of the one or more tensioners.

It is preferred to have a crane, preferably an offshore mast crane,provided on deck for performing various operations on deck, as well asfrom and to the vessel. The capacity of such crane may be severalhundreds of tons. In preferred embodiments, the crane is used to movelarge objects to the pipeline launch trajectory.

A fifth aspect of the invention relates to a marine pipelineinstallation system, preferably for laying an offshore pipeline and/orinstalling a subsea riser. Such a system comprises a vessel, whichvessel may be suitable to carry out the reel lay method, laying rigid orflexible pipelines, but may also be suitable to carry out the J-laymethod.

The system further comprises a pipeline launch tower comprising pipelaying equipment defining a tower firing line, which tower is mountedpivotably on said vessel. The tower is adapted for launching thepipeline in the firing line in the direction of the seabed in a firstposition of the tower in which the tower is at an angle α with respectto the vertical. In the first position of the tower the tower may beinclined at a range of angles below vertical, allowing the launch ofpipeline in many positions of the tower. The inclination α may be in therange between 0 and 70°, more preferably between 0 and 15°, whereby aninclination of 0° corresponds to a vertical orientation of the pipelinelaunch tower.

The pipe laying equipment may comprise tensioners, e.g. when the toweris used for reel laying operations, and may furthermore include weldingstations and line-up tools, e.g. when the tower is used for J-layoperations. Furthermore, the pipe laying equipment may include clampssuch as a hang off module clamp provided in a hang off module.

Such a tower is often placed adjacent or over a moonpool of the vessel,or at another suitable location, e.g. at the stern of the vessel. Ingeneral the term tower here refers to a raised structure on the vessel,and may e.g. be designed as a reel lay ramp. Alternatively or inaddition, the tower may be formed by an A-frame.

The pipeline launch tower supports an abandonment and recovery (A&R)system comprising at least one A&R cable and a sheave arrangement,comprising one or more A&R sheaves. Such A&R sheave arrangement can beused for lowering the launched pipeline, accessories, or launchedpipeline provided with an accessory. Examples of such accessories arepipeline end terminals (PLET's) and connectors. At least one A&R sheaveis provided at an upper position of the pipeline launch tower, allowingthe handling of large objects on deck. Most conventional marine pipelineinstallation systems provide the entire A&R sheave arrangement at anupper position of the pipeline launch tower, such that the accessory ispositionable below the sheave arrangement. Alternatively, the entire A&Rsheave arrangement is positioned at an intermediate position in thetower, or not supported by the pipeline launch tower at all.

The fifth aspect of present invention aims to provide an improved marinepipelaying system, or at least an alternative system.

The present invention provides according to the fifth aspect thereofrelates to an abandonment and recovery sheave arrangement wherein one ormore sheaves of the A&R sheave arrangement are provided at an upperposition of the pipeline launch tower, and one or more other sheaves ofthe A&R sheave arrangement are provided on an A&R trolley which issupported by the pipeline launch tower and moveable substantiallyparallel to the tower firing line. Preferably, an A&R trolley rail isprovided at the pipeline launch tower along which the A&R trolley ismoveable.

With one or more sheaves of the A&R sheave arrangement are provided atan upper position of the pipeline launch tower an accessory ispositionable below the sheave arrangement and the handling of largeobjects on deck is possible.

Most conventional marine pipeline installation systems provide theentire A&R sheave arrangement at an upper position of the pipelinelaunch tower, such that the accessory is positionable below the sheavearrangement. However, this would cause A&R wires to scrap along the rampor edges of the vessel, or, when the pipeline launch trajectory passes amoonpool, along the edges of the moonpool, even with small off lead andside lead angles.

To prevent this, according to the fifth aspect of the invention an A&Rtrolley is provided that guides the wires from the upper A&R sheavesalong the pipeline launch tower. The trolley allows restraining of theA&R wire at a lower position than at an upper position of the pipelinelaunch tower, increasing vessel stability significantly.

Preferably, the trolley can be locked in its lowest position, forexample with pins, to take the full A&R off lead and side lead forces.

In a preferred embodiment, an A&R trolley winch with a constant tensioncontrol (heave compensation) is provided to move the A&R trolley alongthe pipeline launch tower. Such a dedicated winch with a constanttension control preferably fully compensates heave of the vessel. Thismay in particular be advantageous in an arrangement when two A&R winchesare used simultaneously, whereby the wire of one of the winches isreeved through an equalizing sheave and is connected to the wire of thesecond winch. The winches may be operated synchronously by using pulsecounters in the top sheaves. With constant tension control the A&Rtrolley will remain in contact with the equalizing block. Alternatively,the A&R trolley is moved up and down by an A&R hoist associated with theA&R sheave assembly, reducing the A&R hoist capacity due to the weightof the trolley and the sheave efficiencies.

In a preferred embodiment of the invention according to the fifthaspect, the pipeline launch tower is pivotable to a second position inwhich the tower is at an angle β with respect to the vertical, whichangle β is opposite to angle α, in which second position the pipelinecan also be launched from a storage reel into the sea. In the secondposition the tower may be inclined at a range of angles below vertical,opposite to the first position.

Thus, where a tower positioned at an edge of the vessel (the bow, thestern or a side of the vessel) is pivoted to include an acute angle withthe deck in the first position, in the second position the towerincludes an obtuse angle with the deck. Analogously, the tower mayinclude an obtuse angle with the deck in the first position and an acuteangle in the second position. In a preferred embodiment, the pipelinelaunch tower is positioned at the stern of the vessel and is pivotablebetween a position in which the tower is positioned inclined withrespect to the bow with 65° to a second position in which the tower isleaning backwards and extending over the stern with 15°.

In a preferred embodiment according to the fifth aspect of the inventionthe marine pipeline installation further comprises a hang off module forclamping and supporting the weight of previously launched pipelinesupported below the lowermost position of the A&R trolley.

A sixth aspect of the invention relates to a marine pipelineinstallation system, preferably for laying an offshore pipeline and/orinstalling a subsea riser. Such a system comprises a vessel having a bowand a stern, which vessel may be suitable to carry out the reel laymethod, laying rigid or flexible pipelines, but may also be suitable tocarry out the J-lay method.

The system further comprises a pipeline launch tower comprising pipelaying equipment defining a tower firing line, which tower is mountedpivotably on said vessel. The tower is adapted for launching thepipeline in the firing line in the direction of the seabed in a firstposition of the tower in which the tower is at an angle α with respectto the vertical. The pipe laying equipment may comprise tensioners, e.g.when the tower is used for reel laying operations, and may furthermoreinclude welding stations and line-up tools, e.g. when the tower is usedfor J-lay operations. Furthermore, the pipe laying equipment may includeclamps such as a hang off module clamp provided in a hang off module.

Such a tower is often placed adjacent or over a moonpool of the vessel,or at another suitable location, e.g. at the stern of the vessel. Ingeneral the term tower here refers to a raised structure on the vessel,and may e.g. be designed as a reel lay ramp. Alternatively or inaddition, the tower may be formed by an A-frame.

A hang off module is supported in the lower part of the firing line tosupport a previously launched pipeline. Such a hang off module may beallowed to engage with the launched pipeline, e.g. by clamping. In apossible embodiment, the hang off module is supported by the vessel andcomprises associated hang off module pivoting means to pivot the hangoff module together with or independent of the tower. In an alternativeembodiment, the hang off module is supported by the pipeline launchtower and is pivotable together with the tower.

The pipeline launch tower supports an abandonment and recovery (A&R)system comprising at least one A&R cable and a sheave arrangement,comprising one or more A&R sheaves. Such A&R system can be used forlowering the launched pipeline, accessories, or launched pipelineprovided with an accessory. Examples of such accessories are pipelineend terminals (PLET's) and connectors. Preferably, the A&R sheavearrangement is provided at an upper position of the pipeline launchtower, such that the accessory is positionable below the sheavearrangement.

The sixth aspect of present invention aims to provide an improved marinepipelaying system, or at least an alternative system. The inventionfurther aims to provide improved pipeline installation methods.

According to the sixth aspect of the invention the A&R system is mountedto the tower essentially opposite the pipe laying equipment such that itdefines an A&R line remote and opposite from the tower firing line.Further, according to the sixth aspect of the invention the hang offmodule is displaceable by hang off module displacement means from itsposition in the tower firing line to a position in the A&R line.

This allows the A&R system to operate remote from the firing line. Thisis in particular beneficial when the space available in the tower firingline is limited, and large accessories are to be handled. Preferably,the A&R line extends well beyond the stern or the bow of the vessel, orbeyond the gangways. It is envisaged that at least a few decimetersdistance is created between the tower firing line and the A&R line.Large, oversized accessories such as PLETs, which e.g. do not fit inbetween the legs of the pipeline launch tower or ramp may thus beinstalled at a remote launch trajectory: the A&R line. As it ispreferred to assemble accessories in the pipeline, the launched pipelinehas to be translated into the A&R line, which is achieved bydisplacement of the hang off module with the launched pipeline by thehang off module displacement means. Thus, the trajectory in which thepipeline is launched is displaced from the tower firing line to the A&Rline.

In a preferred embodiment of the invention according to the sixthaspect, the pipeline launch tower is pivotable to a second position inwhich the tower is at an angle β with respect to the vertical, whichangle β is opposite to angle α, in which second position the pipelinecan also be launched from a storage reel into the sea. In the secondposition the tower may be inclined at a range of angles below vertical,opposite to the first position.

Thus, where a tower positioned at an edge of the vessel (the bow, thestern or a side of the vessel) is pivoted to include an acute angle withthe deck in the first position, in the second position the towerincludes an obtuse angle with the deck. Analogously, the tower mayinclude an obtuse angle with the deck in the first position and an acuteangle in the second position. In a preferred embodiment, the pipelinelaunch tower is positioned at the stern of the vessel and is pivotablebetween a position in which the tower is positioned inclined withrespect to the bow with 65° to a second position in which the tower isleaning backwards and extending over the stern with 15°.

An advantage of combining the fourth and sixth aspect of the inventionis that it is possible to alter the A&R line by changing the inclinationof the pipeline launch tower. This way, the distance between the A&Rline and the tower firing line that has been used for launching thepipeline may be increased up to several meters. Rotating the pipelinelaunch tower enables the A&R line to extend well beyond the stern of thevessel, facilitating A&R operation such as the lowering of an accessoryover the stern of the vessel, so that the accessory can easily pass thestern of the vessel.

Accessories may be stored on the deck area or alternatively on a barge.Such accessories are positioned in the A&R line, e.g. by a crane or anaccessory handling device, or by mounting the accessories on specialpallets which can skid over rails, or by a combination thereof. Theaccessory may be delivered to the accessory handling device by a crane,such as an offshore mast crane or a knuckle boom crane, or via an A&Rcable in the A&R system. Possibly also the accessory handling device isskiddable into the A&R line.

Preferably, after the accessory is positioned in the A&R line, theaccessory is lined up with the launched pipeline which is supported bythe hang off module, e.g. using the accessory handling device or using adedicated line-up tool (LUT), after which it can be welded to thelaunched pipeline. Alternatively, the PLET may be connected to a tailpipe yet to be launched.

According to a preferred embodiment, the A&R system comprises twosheaves and two wires, one of which is reeved through the pipelinelaunch trajectory while the other is reeved through the A&R line. Thisfacilitates a reasonable A&R capacity in both firing lines.

Preferably the hang off module displacement means comprise a pair ofrails substantially parallel to the deck and substantially parallel tothe intended direction of movement of the vessel during pipelaying alongwhich the hang off module can be translated from the tower firing lineto the A&R line. Actuation means such as cylinders are preferablyprovided, though alternative actuation means are also conceivable.

It is preferred for such pipeline installation vessels to have a crane,preferably an offshore mast crane, provided on deck for performingvarious operations on deck, as well as from and to the vessel. Thecapacity of such crane may be several hundreds of tons. In preferredembodiments, the crane is used to move large objects to the pipelinelaunch trajectory.

In a preferred embodiment, the marine pipelaying system according to thesixth aspect of the present invention further comprises an abandonmentand recovery sheave arrangement of which one or more sheaves areprovided at an upper position of the pipeline launch tower, and one ormore other sheaves of the A&R sheave arrangement are provided on an A&Rtrolley which is supported by the pipeline launch tower and moveablesubstantially parallel to the tower firing line. This embodiment furtherbenefits from the advantages enumerated with respect to the fifth aspectof the invention above.

The above described marine pipeline installation system according to thesixth aspect of the invention is suitable for an exemplary A&R accessoryhandling operation in which an accessory is installed in the pipeline,which method comprises the following steps:

-   -   launching the pipeline in the tower firing line into the sea        from the first position of the tower in which the tower is at an        angle α with respect to the vertical,    -   stopping the launch of pipeline, and hanging off the launched        pipeline in the hang off module,    -   displacing the hang off module with the launched pipeline from        its position in the tower firing line to a position in the A&R        line by the hang off module displacement means,    -   positioning the accessory in the A&R line,    -   attaching the accessory to the launched pipeline in the hang off        module and to the at least one A&R cable,    -   suspending the accessory and the launched pipeline from the A&R        system,    -   disengaging the hang off module from the launched pipeline,    -   displacing the hang off module from its position in the A&R line        to a position in the tower firing line by the hang off module        displacement means,    -   lowering the accessory with the launched pipeline by the A&R        system.

In a preferred embodiment the pipeline launch tower or the marinepipeline installation system according to the sixth aspect of theinvention the pipeline launch tower is pivotable to a second position inwhich the tower is at an angle β with respect to the vertical, whichangle β is opposite to angle α, in which second position the pipelinecan also be launched into the sea.

An advantage of combining the fourth and sixth aspect of the inventionis that it is possible to alter the A&R line by changing the inclinationof the pipeline launch tower. This way, the distance between the A&Rline and the tower firing line that has been used for launching thepipeline may be increased up to several meters. Rotating the pipelinelaunch tower enables the A&R line to extend well beyond the stern of thevessel, facilitating A&R operation such as the lowering of an accessoryover the stern of the vessel, so that the accessory can easily pass thestern of the vessel.

As such, the marine pipeline installation system according to the fourthand sixth aspect of the invention is suitable for an exemplary A&Raccessory handling operation in which an accessory is installed in thepipeline, which method comprises the following steps:

-   -   launching the pipeline in the tower firing line into the sea        from the first position of the tower in which the tower is at an        angle α with respect to the vertical,    -   stopping the launch of pipeline, and hanging off the launched        pipeline in the hang off module,    -   pivoting the pipeline launch tower to a second position in which        the tower is at an angle β with respect to the vertical,    -   displacing the hang off module with the launched pipeline from        its position in the tower firing line to a position in the A&R        line by the hang off module displacement means,    -   positioning the accessory in the A&R line,    -   attaching the accessory to the launched pipeline in the hang off        module and to the at least one A&R cable,    -   suspending the accessory and the launched pipeline from the A&R        system,    -   disengaging the hang off module from the launched pipeline,    -   displacing the hang off module from its position in the A&R line        to a position in the tower firing line by the hang off module        displacement means,    -   lowering the accessory with the launched pipeline by the A&R        system.

When the accessory has passed the stern of the vessel the tower may berotated back and the accessory can be lowered further to the seabed inthe modified A&R line, which has been rotated together with the tower.Possibly the launched pipeline with the PLET is now abandoned to obtaina new stock of pipes or pipeline.

Preferably, the accessory is provided with a pipe end portion. Then,when the accessory has passed the stern of the vessel, the accessory ishang off module by the hang off module. The hang off module withsuspended accessory, possibly a PLET connected to a launched pipeline,may subsequently be translated from the A&R line to the tower firingline. The above method is then followed by the following steps:

-   -   launching the accessory and the launched pipeline by the A&R        cable until the pipe end portion is at the same height level as        the position of the hang off module,    -   displacing the hang off module from its position in the tower        firing line to a position in the A&R line by the hang off module        displacement means,    -   engaging the pipe end portion to the hang off module,    -   detaching the A&R cable from the accessory.

Now, the accessory and the launched pipeline are supported by the hangoff module in the A&R line. Possibly, the hang off module issubsequently displaced back to its position in the tower firing linewhere another pipeline is attached to the pipe end portion andpipelaying continues.

The marine pipeline installation system according to the fourth andsixth aspect of the invention is further suitable for transferring alaunched pipeline from a first marine pipeline installation system to asecond marine system which comprises a winch and a cable. Such methodpreferably comprises the following steps:

-   -   launching the pipeline into the sea from the first position of        the tower in which the tower is at an angle α with respect to        the vertical,    -   stopping the launch of pipeline, and hanging off the launched        pipeline in the hang off module,    -   pivoting the pipeline launch tower to the second position in        which the tower is at an angle β with respect to the vertical,    -   attaching both the at least one A&R cable and the cable of the        second marine system to the launched pipeline,    -   suspending the launched pipeline from the A&R system,    -   disengaging the hang off module from the launched pipeline,    -   launching the launched pipeline by the at least one A&R cable        until the cable of the second marine system is taut,    -   detaching the at least one A&R cable from the launched pipeline        and support the launched pipeline from the winch of the second        marine system.

A seventh aspect of the invention relates to a method for transferring alaunched pipeline from a first marine pipeline installation system to asecond marine system which comprises a winch and a cable.

The first marine pipeline installation system comprises:

-   -   a vessel,    -   a pipeline launch tower comprising pipe laying equipment        defining a tower firing line, which tower is mounted pivotably        on said vessel and which is adapted for launching the pipeline        along the firing line into the sea in a first position of the        tower in which the tower is at an angle α with respect to the        vertical and wherein the pipeline launch tower is pivotable to a        second position in which the tower is at an angle β with respect        to the vertical, which angle β is opposite to angle α in which        second position the pipeline can also be launched into the sea,    -   a hang off module supported in the lower part of the firing line        for clamping and supporting the weight of previously launched        pipeline,    -   an abandonment and recovery (A&R) system comprising at least one        A&R cable and a sheave arrangement with one or more sheaves        provided at an upper position in the firing line.

Such marine pipeline installation systems are well known in the art,preferably for laying an offshore pipeline and/or installing a subseariser. Such a system comprises a vessel having a bow and a stern, whichvessel may be suitable to carry out the reel lay method, laying rigid orflexible pipelines, but may also be suitable to carry out the J-laymethod.

The system further comprises a pipeline launch tower comprising pipelaying equipment defining a tower firing line, which tower is mountedpivotably on said vessel. The pipe laying equipment may comprisetensioners, e.g. when the tower is used for reel laying operations, andmay furthermore include welding stations and line-up tools, e.g. whenthe tower is used for J-lay operations. Furthermore, the pipe layingequipment may include clamps such as a hang off module clamp provided ina hang off module.

Such a tower is often placed adjacent or over a moonpool of the vessel,or at another suitable location, e.g. at the stern of the vessel. Ingeneral the term tower here refers to a raised structure on the vessel,and may e.g. be designed as a reel lay ramp. Alternatively or inaddition, the tower may be formed by an A-frame.

A hang off module is supported in the lower part of the firing line tosupport a previously launched pipeline. Such a hang off module may beallowed to engage with the launched pipeline, e.g. by clamping. In apossible embodiment, the hang off module is supported by the vessel andcomprises associated hang off module pivoting means to pivot the hangoff module together with or independent of the tower. In an alternativeembodiment, the hang off module is supported by the pipeline launchtower and is pivotable together with the tower.

The pipeline launch tower supports an abandonment and recovery (A&R)system comprising at least one A&R cable and a sheave arrangement,comprising one or more A&R sheaves. Such A&R system can be used forlowering the launched pipeline, accessories, or launched pipelineprovided with an accessory. Examples of such accessories are pipelineend terminals (PLET's) and connectors. Preferably, the A&R sheavearrangement is provided at an upper position of the pipeline launchtower, such that the accessory is positionable below the sheavearrangement.

The seventh aspect of present invention aims to provide an improvedmethod for transferring a launched pipeline from a first marine pipelineinstallation system to a second marine system which comprises a winchand a cable, or at least an alternative method.

The method according to the seventh aspect of the invention comprisesthe following steps:

-   -   launching the pipeline into the sea from the first position of        the tower in which the tower is at an angle α with respect to        the vertical,    -   stopping the launch of pipeline, and hanging off the launched        pipeline in the hang off module,    -   pivoting the pipeline launch tower to the second position in        which the tower is at an angle β with respect to the vertical,    -   attaching both the at least one A&R cable and the cable of the        second marine system to the launched pipeline,    -   suspending the launched pipeline from the A&R system,    -   disengaging the hang off module from the launched pipeline,    -   launching the launched pipeline by the at least one A&R cable        until the cable of the second marine system is taut,    -   detaching the at least one A&R cable from the launched pipeline        and support the launched pipeline from the winch of the second        marine system.

Such method is in particular beneficial for handing over pipeline andaccessories that are bulky and/or heavy in weight.

It will be clear for the skilled person that the various aspects of theinvention can be realized separately and/or in all possiblecombinations.

The present invention will be explained in greater detail with referenceto the figures, in which:

FIGS. 1a-1e schematically show a marine pipeline installation system forperforming a method for installing an accessory according to the firstaspect of the invention;

FIGS. 2a-2b schematically show an alternative method for installing anaccessory according to the first aspect of the invention;

FIGS. 3a-3b schematically show a second alternative method forinstalling an accessory according to the first aspect of the invention;

FIGS. 4a-4b schematically show a third alternative method for installingan accessory according to the first aspect of the invention;

FIGS. 5a-5d show a detail of a marine pipeline installation systemaccording to a second aspect of the invention;

FIGS. 6a-6c show a detail of a marine pipeline installation systemaccording to a third aspect of the invention;

FIGS. 7a-7c schematically show an alternative detail of a marinepipeline installation system according to a third aspect of theinvention;

FIG. 8 shows a side view of a reel-lay pipeline installation accordingto the fourth, fifth and sixth aspect of the present invention;

FIG. 9 shows the reel-lay pipeline installation of FIG. 8 in threepositions according to the fourth aspect of the present invention,

FIG. 10 shows the reel-lay pipeline installation of FIG. 8 in a rearview,

FIG. 11 shows a stern of a floating vessel at least suitable for thereel lay method according to the seventh aspect of the invention;

FIGS. 12a-12e show part of the stern of a floating vessel according toFIG. 11.

In FIG. 1a is shown a marine pipeline installation system for laying anoffshore pipeline comprising a vessel 202 with a hull 201, suitable tocarry out the method according to the first aspect of the invention. Inthe hull 201 a moonpool 235 is provided at the stern of the vessel 202.Above the moonpool 235 is positioned a pipeline launch tower 206 havingpipe laying equipment defining a tower firing line 204. The tower 206 ismounted pivotably on said vessel 202 and is adapted for launching apipeline 231 along the tower firing line 204 into the sea in a firstposition X of the tower 206 in which the tower 206 is at an angle α withrespect to the vertical. Adjustable connecting arm 207 adjusts andmaintains the inclination of tower 206.

The marine pipeline installation system further comprises a hang offmodule 210 supported in the lower part of the tower firing line 204 forclamping and supporting the weight of the previously launched pipeline231. In this embodiment, the hang off module 210 is pivotable togetherwith tower 206.

An abandonment and recovery (A&R) system is provided comprising an A&Rcable 213 and a sheave arrangement 212 with one or more sheaves providedat an upper position in the tower firing line 204. In FIG. 1a , A&Rcable 213 is aligned along tower firing line 204.

The marine pipeline installation system further comprises an accessoryhandling device for positioning an accessory 232 between the hang offmodule 210 and the A&R sheave arrangement 212 in the tower firing line204. For clarity reasons, this accessory handling device is omitted inFIG. 1a -1 e.

FIG. 1a shows the accessory 232, here comprising two pipe end portions233 and 234. The pipe end portions 233 and 234 can be connected to thepreviously launched pipeline 231 or to other pipe sections. Duringnormal operation, the marine pipeline installation system launches thepipeline 231 from the first position of the tower 206 with respect tothe vertical, in a pipeline launch trajectory corresponding to the towerfiring line 204 into the sea. To install accessory 232 onto the pipeline231, the launch of the pipeline 231 is stopped, and the launchedpipeline 231 is hang off module in hang off module 210, as shown in FIG.1 a.

The accessory handling device, which is not shown in FIG. 1a-1e ,subsequently positions the accessory 232 with pipe end portions 233 and234 in the tower firing line 204 between the hang off module 210 and theA&R sheave assembly 212, as shown in FIG. 1b . In this embodiment,accessory 232 with pipe end portions 233 and 234 is positioned such thatpipe end portion 234 is adjacent to the pipeline 231. An upside downorientation of accessory 232 with pipe end portions 233 and 234 is alsopossible.

In this embodiment, the pipe end portion 234 is attached to the launchedpipeline 231 in the hang off module 210 and pipe end portion 233 isattached to A&R cable 213. It is also conceivable that an accessory 232without pipe end portions 233 and 234 is installed on the pipeline 231.In that case, the accessory 232 is connected directly to pipeline 231and the A&R cable 213 is also attached directly to the accessory 232.

A&R cable 213 is now hauled in until A&R cable 213 is taut and theaccessory 232 with pipe end portions 233 and 234, and pipeline 231 aresuspending from the A&R system. This allows the save disengagement ofthe launched pipeline 231 from the hang off module 210.

In FIG. 1c , the connecting arm 207 has been adjusted such that thetower 206 is pivoted to an accessory launch position Y in which thetower 206 is at an angle γ with respect to the vertical. The pipeline231 in this position of the tower is considered to stay at the launchtrajectory which is at an angle α as shown in FIG. 1c . In thisembodiment, the angle between the tower firing line 204 of the tower 206and the pipeline 231 is γ-α. However, due to the rotation to theaccessory launch position and/or movement of the vessel 202, the anglebetween the pipeline 231 and the vertical can be different resulting ina different angle between the tower firing line 204 and the pipeline231. Important for the launch of the accessory 232 is that angle γdiffers substantially from angle α, so that a pipeline launch trajectoryis created which is large enough for the accessory 232 with the pipe endportions 233 and 234 and the pipeline 231 to be launched with the A&Rsystem at a distance from the tower 206. This is in particularbeneficial when the space available in the tower firing line 204 islimited and large accessories are to be handled which can not passthrough hang off module 210.

In FIG. 1d , the accessory 232 with pipe end portions 233 and 234,together with pipeline 231 is launched into the sea by the A&R system.The accessory 232 passes hang off module 210 at a distance thereof andis lowered through moonpool 235. It is conceivable that the pipeline 231with the attached accessory 232 and pipe end portions 233 and 234 isabandoned and recovered later. Alternatively, as is shown in FIG. 1d ,the accessory with pipe end portions 233 and 234, and pipeline 231 arelaunched by the A&R cable 213 until pipe end 233 is at the same heightlevel as the position of the hang off module 210.

The connecting arm 207 is then adjusted such that the pipeline launchtower 206 is pivoted back to the first position X in which the tower 206is at an angle α with respect to the vertical, such that the trajectoryof the pipeline 231 again coincides with the tower firing line 204 ofthe tower, as shown in FIG. 1e . The pipe end portion 233 is allowed toengage with hang off module 210, such that the accessory with pipe endportions 233 and 234, and pipeline 231 suspend from the hang off module210. The A&R cable 213 can now be detached from pipe end portion 233 toallow new pipe sections to be connected to the pipe end portion 233.

In the method shown in FIG. 1a-1e , tower 206 is pivoted from a firstposition X with an acute angle α with respect to the vertical towardsthe bow of the vessel 202 to an accessory launch position Y in thedirection of the bow of the vessel 202 in which the tower 206 has a lessacute angle γ with respect to the vertical towards the bow of the vessel202.

However, many variants are possible.

FIGS. 2a and 2b show a vessel 302 without a moonpool, provided with apipeline launch tower 306 at the stern of the vessel 302. In FIG. 2a afirst position X′ of the tower 306 is shown having an angle α withrespect to the vertical away from the bow of the vessel 302. FIG. 2bshows an accessory launch position Y′, wherein the tower 306 has anangle γ with respect to the vertical towards the bow of the vessel 302.

FIGS. 3a and 3b show another variant with respect to the two positions Xand Y of a pipeline launch tower. FIG. 3a shows a vessel 402 providedwith a pipeline launch tower 406 in a first position X″ with the tower406 having an angle α with respect to the vertical towards the bow ofthe vessel 402. FIG. 3b shows said tower 406 in an accessory launchposition Y″, wherein the tower 406 has substantially no angle γ withrespect to the vertical and is thus positioned substantially vertically.

In yet another variant with respect to the two positions X and Y of apipeline launch tower, FIG. 4a shows a vessel 502 provided with apipeline launch tower 506 in a first position X″′ with the tower 506having an angle α with respect to the vertical away from the bow of thevessel 502. FIG. 4b shows said tower 506 in an accessory launch positionY″′, wherein the tower 506 has an angle γ with respect to the verticalfurther away from the bow of the vessel 502.

It is conceivable that more variants are possible such as embodimentswhere the tower is positioned at a side of the vessel. The flexibilityof such a marine pipeline installation system allows the system to adaptthe angle of the pipeline launch trajectory and also allows the launchof an accessory onto the pipeline when little space is available.

Furthermore is it conceivable that the method and variants shown in theFIGS. 1-4 are also possible with positions X and Y of the pipelinelaunch tower having an obtuse angle with the vertical instead of theshown acute angles. Also combinations of acute and obtuse angles arepossible.

In FIGS. 5a to 5d is shown a part of a marine pipeline installationsystem for laying an offshore pipeline according to the second aspect ofthe invention.

The marine pipeline installation system according to the second aspectof the invention comprises a vessel, which is not shown in either of theFIGS. 5a-5d . The system further comprises a pipeline launch tower 606attached to said vessel, of which only the lower part is shown in FIGS.5a-5d . The pipeline launch tower 606 comprises pipe laying equipmentdefining a tower firing line 604. The tower 606 is mounted pivotablyabout a tower pivot axis on said vessel and is adapted for launching apipeline 631 in the tower firing line 604 into the sea at least in afirst position of the tower 606 in which the tower is at an angle α withrespect to the vertical, as shown in FIG. 5 b.

The marine pipeline installation system further comprises a workstation660 supported in the lower part of the pipeline launch tower 606, theworkstation 660 comprising a working platform 661 supported by a supportframe 663 as shown in FIG. 5a . This working platform 661 is accessibleto personnel 662 (see FIG. 5b ) to perform inspection operations etc.

Furthermore, the marine pipeline installation system comprises a hangoff module (not shown) supported by the support frame 663 in the lowerpart of the tower firing line 604 for clamping and supporting the weightof previously launched pipeline 631.

The workstation 660 further comprises a support frame guide (670)substantially perpendicular to the tower pivot axis and substantiallyperpendicular to the tower firing line 604 along which the support frame663 is skiddable, such that the working platform 661 and the hang offmodule are skiddable into and out of the tower firing line 604,indicated by the arrow T in FIGS. 5a and 5 b.

FIG. 5a shows the working platform 661 in a position, in which theworking platform 661 is positioned out of the tower firing line 604. Inthis way, the working platform 661 does not interfere with passingaccessories or thickenings of the pipeline 631.

FIG. 5b shows the working platform 661 in a position, in which theworking platform 661 is positioned into the tower firing line 604. Ascan be seen, personnel 662 can get near the pipeline 631 through workingplatform 661. In this embodiment, the working platform 661 is positionedhorizontally, such that personnel 662 can naturally walk around workingplatform 661.

FIGS. 5c and 5d show the pipeline launch tower 606 at other angles withrespect to the vertical, respectively at a substantially verticalposition of the tower 606 in FIG. 5c , and at an angle opposite to angleα of FIG. 5b in FIG. 5d . Also in these positions the working platformstays in a horizontal position. This is possible because between thetrolley 663 and the working platform 661 a platform axis 664 parallel tothe tower pivot axis is provided. This enables the working platform 661to gimbal maintaining a horizontal position independent of the positionof the tower 606. A relative movement of the working platform 661 withrespect to the tower 606 can be achieved by gimbal means comprisingpreferably a cylinder or a gear wheel with motor.

FIG. 5a also shows that working platform 661 comprises two platformportions 661 a and 661 b between which a swinging axis parallel to thetower pivot axis is provided, such that the platform portion 661 bclosest to the tower firing line 604 can be swung back so as to clearthe area around the tower firing line 604 when the working platform 661is in the position out of the tower firing line 661. In this embodiment,the swinging axis coincides with platform axis 664. It is alsoconceivable that the swinging axis is located elsewhere, e.g. betweenplatform axis 664 and the end of platform portion 661 b.

FIGS. 6a-6c show a part of a marine pipeline installation system forlaying an offshore pipeline comprising a vessel (not shown) and apipeline launch tower (also not shown). As shown in FIG. 6a , the towercomprises pipe laying equipment defining a tower firing line 704, whichtower is mounted pivotably about a tower pivot axis on said vessel andwhich is adaptable for launching a pipeline (not shown) in the towerfiring line 704 into the sea in a first position of the tower in whichthe tower is at an angle α with respect to the vertical. The inclinationα may be in the range between 0 and 70°, more preferably between 0 and15°, whereby an inclination of 0° corresponds to a vertical orientationof the pipeline launch tower. In the FIGS. 6a-6c , the tower ispositioned in a substantially vertical position in which α is 0°.

The system further comprises an abandonment and recovery (A&R) systemcomprising at least one A&R cable 713 and a sheave arrangement with oneor more sheaves supported by the pipeline launch tower. In thisembodiment, two sheaves 770, 771 are supported by a support frame 763.The support frame 763 is skiddable along a support frame guide (740)provided in a lower part of the pipeline launch tower, which guide issubstantially perpendicular to the tower pivot axis and substantiallyperpendicular to the tower firing line 704, such that the two sheaves770, 771 are skiddable into and out of the tower firing line 704.

Furthermore, FIG. 6a shows a hang off module 710 supported in the lowerpart of the tower firing line 704 for clamping and supporting the weightof previously launched pipeline. Not shown in this embodiment is thatthe hang off module 710 is supported by the support frame 763, such thatthe hang off module 710 is skiddable into and out of the tower firingline 704, together with the sheaves 770,771.

Sheave 770 is not moveable with respect to support frame 763 and canonly rotate about its own sheave pivot axis 741 substantially parallelto the tower pivot axis. On the other hand, sheave 771 is movablysupported by the support frame 763 by mechanism 772, such that thesheave 771 is movable in a direction substantially parallel to the towerpivot axis. Sheave 771 is in FIG. 6a lined up with A&R cable 713 toguide the A&R cable 713.

In FIG. 6a , the support frame is located in a workstation 760. Thisworkstation 760 further comprises a working platform 761 also supportedby the support frame 763, such that the working platform 761 isskiddable into and out of the tower firing line 704. The workingplatform 761 is accessible to personnel to perform inspection operationsetc.

Between the support frame 763 and the working platform 761 a platformpivot axis 764 parallel to the tower pivot axis is provided, such thatthe working platform 761 can gimbal maintaining a substantiallyhorizontal position independent of the position of the tower. Thisrelative movement between the working platform 761 and the tower isachieved by gimbal means, which comprise for instance a cylinder or agear wheel and motor (not shown).

Further, the working platform 761 comprises two platform portions 761 aand 761 b between which a swinging axis parallel to the tower pivot axisis provided, such that the platform portion 761 b closest to the towerfiring line 704 can be swung back so as to clear the area around thetower firing line 704. In this embodiment, the swinging axis coincideswith platform pivot axis 764. It is also conceivable that the swingingaxis is located between platform axis 764 and the end of platformportion 761 b.

A slot 767 is provided in platform portion 761 b to receive the A&Rcable 713 or a pipeline and enable an almost 360° inspection area.

The advantage of the support frame 763 being skiddable into and out ofthe tower firing line 704 is that in case of the passage of an accessoryor thickening in the pipeline, the support frame 763 can be moved toclear the area around the tower firing line 704, such that the workingplatform 761, hang off module 710 and sheaves 770 and 771 do notinterfere with the passing of the accessory or thickening in thepipeline.

In FIG. 6b , another configuration of the system of FIG. 6a is shown.The A&R system has been adapted to a double fall system and comprisestwo A&R cables 713 a and 713 b. In this way, the load suspended by theA&R system is divided over two A&R cables 713 a and 713 b and heavierloads can be suspended. The two A&R cables 713 a and 713 b are connectedto each other and run over an equilizing sheave 773.

The support frame 763 has been skidded to a position in which the A&Rcables 713 a and 713 b are guided by an opposite side of the sheaves 770and 771 than the sheave 771 shown in FIG. 6a . Also, sheave 771 hasmoved in a direction substantially parallel to the tower pivot axis, tobe ligned up with A&R cable 713 b. Preferably, the A&R cables 713 a and713 b are placed symmetrically with respect to the tower firing line704.

FIG. 6c shows sheaves 770 and 771 are positioned in the double fallsystem, such that sheave 770 guides A&R cable 713 a, and sheave 771guides cable 713 b. In FIG. 6c support frame 763 has skidded such thatboth sheaves 770 and 771 guide the A&R cables 713 a and 713 b at anopposite side of the sheave as shown in FIG. 6 b.

FIG. 7a shows an alternative support frame 863 movably supporting twosheaves 870 and 871 to be used in a marine pipeline installation systemfor laying an offshore pipeline according the third aspect of theinvention.

The sheaves 870 and 871 are used to guide abandonment and recovery (A&R)cables from an A&R system. The support frame is supported in the lowerpart of a pipeline launch tower, which comprises pipe laying equipmentdefining a tower firing line and a tower pivot axis to pivot the tower.The support frame 863 is skiddable along a support frame guide (notshown) substantially perpendicular to the tower pivot axis andsubstantially perpendicular to the tower firing line, as indicated byarrow T′. Sheaves 870 and 871 are supported by support frame 863 throughrespectively mechanisms 874 and 872. These mechanisms 874 and 872 allowa substantially parallel movement to the tower pivot axis of the sheaves870 and 871. This movement is achieved by the actuation of cylinders 875and 876.

In this embodiment, the support frame 863 further comprises a weldingstation 880, which makes the marine pipeline installation system inparticular suitable for the J-lay method.

FIG. 7a shows the sheaves 870 and 871 positioned in a one cable guideposition, wherein sheave 870 is lined up with an A&R cable 813. In thisone cable guide position, the sheave 870 guides the A&R cable 813. It isalso possible for sheave 870 to guide the A&R cable 813 on the otherside of the sheave 870. Which side is required depends on the angle ofthe tower.

Mechanism 874 and 872 are provided with guide blocks 890 andcorresponding guide block cylinders 891 to move the guide blocks. Theguide blocks 890 are movable between a position, wherein the sheaves 870and 871 can receive an A&R cable, and a position wherein an A&R cable islocked up between the sheave 870 or 871 and the guide block 890. Othermeans to move the guide blocks 890 and mechanisms 874 and 872 are alsopossible.

In FIG. 7b , the sheaves 870 and 871 are moved by cylinders 875 and 876to a double fall A&R system, wherein the sheaves 870 and 871 guide twoA&R cables 813 a and 813 b which are placed symmetrically. It is alsopossible that the two sheaves 870 and 871 guide the A&R cables on theother side of the sheaves 870, 871.

FIG. 7c shows a position wherein both sheaves 870 and 871 are misalignedwith A&R cables 813 a and 813 b. In a possible scenario, the supportframe 863 can now move to the left. In this way, sheaves 870 and 871pass the A&R cables 813 a and 813 b. When the sheaves 870 and 871 havepassed the A&R cables 813 a and 813 b, the sheaves 870 and 871 can bemoved back to the two cable guide position as shown in FIG. 7b , withthe difference that the sheaves 870 and 871 are now at the other side ofthe A&R cables. The guide blocks 890 on the right side of the sheavescan be moved by cylinders 891 to lock up the A&R cables 813 a and 813 b.

In FIG. 8 a stern of a floating vessel 2 at least suitable for carryingout the reel lay method is shown, comprising features according to thefourth, fifth and sixth aspect of the invention. The vessel is providedwith a pipeline launch tower 6, which tower 6 is connected pivotally tothe vessel 2 by hinge part 8, defining an essentially horizontal pivotaxis. The inclination of the tower 6 is adjustable and can be maintainedby connecting arm 7 and adjusters 8. The tower comprises pipe layingequipment defining a firing line 4 along which a pipe may be launched,at least from a first position of the tower in which the tower is at anangle with respect to the vertical.

Near the top of the tower 6 a pipeline guide wheel 3 or other guidestructure is mounted, which serves to guide the pipeline from a storagereel (not shown here) to the firing line 4 along the tower 6. Duringnormal reel lay operation continuous pipeline extends from said guidewheel 3 in said firing line 4 in the direction to the seabed (notshown).

The pipelaying equipment on the tower 6 comprises, in the shownembodiment, two tensioners 5 downstream of the guide wheel 3. Below thelower tensioner 5 a platform 17 is provided in the shown embodiment.Between the upper tensioner 5 and the guide wheel 3 also a pipelinestraightener 9 and a pipeline centralizer 19 are provided. A knuckleboom crane 18 is in this embodiment provided at the top of the tower 6.

In the shown embodiment a hang off module 10 is supported directly fromthe hull of the vessel 2. It could be envisaged that said hang offmodule is mounted at a lower end of the tower 6. The hang off module 10is adapted to support the weight of the previously launched pipeline.

An abandonment and recovery (A&R) system 11 is provided in the pipelinelaunch tower 6, here it is mounted at an upper position thereof. The A&Rsystem 11 comprises multiple sheaves 12 and multiple A&R cables 13. TheA&R system 11 is operated by A&R winches 14 provided on the vessel 2.Redundant A&R cable 13 may be stored in A&R storage 15 in the vessel 2and guided to winches 14 via sheave 16.

In the shown embodiment, an optional crane 20 is provided. This isclearly shown in the rear view of FIG. 10 in which a pipe section 30 isheld by the knuckle boom crane 20 in the firing line 4. Such crane 20may also be used for accessory handling, e.g. for positioning anaccessory in the firing line of the tower.

According to the fourth aspect of the invention, the pipeline launchtower 6 is pivotable between a first position in which the tower 6 ispositioned inclined at an angle α with respect to the vertical, and asecond position in which the tower 6 is positioned inclined at an angleβ with respect to the vertical, which angle β is opposite to angle α,which tower 6 allows launching of the pipeline on both extreme andintermediate positions.

In FIG. 9 the reel-lay pipeline installation of FIG. 8 is show in threedifferent positions according to the fourth aspect of the presentinvention: an inclined position A in which the tower 6 is inclined withrespect to the bow and is at an angle α with respect to the vertical, aposition B in which the tower 6 is positioned perpendicular to thevessel 2, hence, with a vertical orientation, and a third position C inwhich the tower 6 is positioned inclined with respect to the stern andis at an angle β with respect to the vertical. In the embodiment of thereel-lay pipeline installation shown in FIGS. 8 and 9, the hang offmodule 10 is supported by the vessel 2. The hang off module is pivotabletogether with the tower 6 via associated hang off module pivoting means21, here embodied as a cylinder.

According to the fifth aspect of the invention a sheave 112 of the A&Rsheave arrangement 11 is provided on a trolley 25 which is supported bythe pipeline launch tower 6 and moveable substantially parallel to thetower firing line 4, in the shown embodiment via rails 26. To the A&Rwire 13 an A&R underwater hook 27 is provided in this embodiment, whichis provided with an equalizing sheave.

Optional tail handling rollers 28 are provided in the A&R line 23, whichmay guide a tail pipe hanging from the pipeline guide 3 yet to belaunched. These tail handling rollers 28 may be pivoted out of the A&Rline 23, via pivot axes 29. In FIGS. 8 and 9, both positions in and outof the A&R line 23 are indicated.

According to the sixth aspect of the invention the A&R sheavearrangement 11 extends from the pipeline launch tower 6 defining an A&Rline 23 remote from and opposite to the tower firing line 4. The hangoff module 10 is displaceable along hang off module rails 24 from aposition in the firing line 4 (as shown in FIG. 8) to a position in theA&R line 23 (not shown).

In FIG. 11 is shown a stern of a floating vessel 102 at least accordingto the seventh aspect of the invention. The shown vessel 102 is at leastsuitable for carrying out the reel lay method. The vessel is providedwith a pipeline launch tower 106, which tower 106 is connected pivotallyto the vessel 102 by hinge part 108, defining an essentially horizontalpivot axis. The tower comprises pipe laying equipment defining a firingline 104 along which a pipe may be launched, at least from a firstposition of the tower in which the tower is at an angle with respect tothe vertical. When the tower 106 is not in operation, the tower 106 canbe pivoted towards the vessel 102, to rest on tower support 141.

Near the top of the tower 106 a pipeline guide wheel 103 or other guidestructure is mounted, which serves to guide the pipeline from a storagereel 142 to the firing line 104 along the tower 106. The pipe layingequipment on the tower 106 comprises, in the shown embodiment, twotensioners 105 downstream of the guide wheel 103. During normal reel layoperation a continuous pipeline extends from the storage reel 142 tosaid guide wheel 103, and from said guide wheel 103 to the tensioners105 in said firing line 104.

In the shown embodiment a hang off module 110 is supported directly fromthe hull of the vessel 102. It could be envisaged that said hang offmodule is mounted at a lower end of the tower 106. The hang off module110 is adapted to support the weight of a previously launched pipeline131. The hang off module 110 comprises pivoting means to pivot the hangoff module together with or independent of the tower 106. The pivotingmeans comprise a cylinder 121 to pivot the hang off module 110.

An abandonment and recovery (A&R) system 111 is provided in the pipelinelaunch tower 106. The A&R system 111 comprises a sheave 212 and an A&Rcable 113. An A&R underwater hook 127 is provided on the cable 113 inthis embodiment. Sheave 212 is mounted at an upper position of thepipeline launch tower 106, remote from and opposite to the tower firingline 104 to form an A&R line 123 according to the sixth aspect of theinvention. However, for performing the method according to the seventhaspect of the invention, a distinct A&R line is not a requisite.

The A&R underwater hook 127 in this embodiment is connected to ahoisting block (not shown), which in FIG. 11 is engaged with a trolley125, according to the fifth aspect. Trolley 125 also is not a requisitefor performing the method according to the seventh aspect of theinvention. A&R cable 113 extends between the hoisting block (not shown)and an A&R winch (not shown). The trolley 125 is movably supported bytower 106, so that the trolley 125 can be moved up and down along thetower 106. When the hoisting block engages with the trolley 125, the A&Runderwater hook 127 is allowed to move together with the trolley 125substantially parallel to the tower 106.

According to the seventh aspect of the invention, the pipeline launchtower 106 is pivotable between a first position in which the tower 106is positioned inclined at an angle α with respect to the vertical (notshown), and a second position in which the tower 106 is positionedinclined at an angle β with respect to the vertical, which angle β isopposite to angle α. The tower 106 in FIG. 11 is positioned in thesecond position.

According to the seventh aspect of the invention, the launched pipeline131 from FIG. 11 can be transferred from the vessel 102 to a secondmarine system 150 as shown in the FIG. 12a-12e . It is conceivable thatsecond marine system 150 is a platform, vessel or other pipelineinstallation system.

During normal reel lay operation, the pipeline 131 is launched into thesea preferably from the first position of the tower 106 in which thetower 106 is at an angle α with respect to the vertical, such as shownin FIG. 9. To initiate the transfer of the pipeline 131 from the vessel102 to the second marine system 150, the launch of the pipeline 131 isstopped and the launched pipeline 131 is hang off module in hang offmodule 110 which is aligned with tower 106, as shown in FIG. 12a .Subsequently, the pipeline launch tower 106 is pivoted to the secondposition in which the tower is at an angle β with respect to thevertical. This position is shown in FIG. 12a and allows the vessel 102to move backwards and approach the second marine system 150.

According to the sixth aspect of the invention, the hang off module 110of this shown embodiment is displaceable along hang off module rails 124from a position in the firing line 104 (as shown in FIG. 12a ) to aposition in the A&R line 123 (as shown in FIG. 12b ). This allows theA&R system 150 to operate remote from the firing line 104. This isadvantageous for instance when the available space in the tower firingline 104 is limited and large accessories are to be handled (not shown).The steps described below are also possible when A&R line 123substantially coincides with firing line 104. Then, the displacement ofhang off module 110 is not a necessary step for transferring thepipeline 131 to the second marine system 150.

In FIG. 12b , the A&R underwater hook 127 has been moved downwards alongthe A&R line 123. The hook 127 is connected to a hoisting block (notshown) which is engaged with the trolley 125. The trolley 125 guides thehoisting block with hook 127, suspended by the A&R cable 113, along A&Rline 123.

In FIG. 12c , a connection cable 155 connects the pipeline 131 to A&Runderwater hook 127, and a cable 151 of the second marine system 150connects the pipeline 131 to the second marine system 150. This is donein such a way that the cable 151 of the second marine system 150 isslack.

In this embodiment, first the A&R winch is actuated such that A&R cable113 is stretched and the pipeline 131 is suspended from the A&R system.Then the hoisting block (not shown) is allowed to disengage from thetrolley 125, and the hang off module 110 disengages from the pipeline131.

In FIG. 12d , the hang off module 110 has been displaced along hang offmodule rails 124 from its position in the A&R line 123 via its positionin the firing line 104 (as shown in FIG. 12a ) to a rest position beyondfiring line 104. In this rest position cylinder 121 is extended suchthat the hang off module 110 is at an angle with the vertical, hereopposite of the angle the tower 106 has with the vertical, to mainlyadapt the orientation of the hang off module to the surface of vessel102. In this way, hang off module 110 makes room in the area below tower106.

The A&R cable 113 is paid out to launch the pipeline 131 until thesecond cable 151 is taut.

In FIG. 12e , the A&R underwater hook 127 is disconnected from the firstcable 155 and the pipeline 131 is now only connected to the secondmarine system 150. A&R cable 113 can now be hauled in by the A&R winch(not shown). It is not shown, but if necessary, second cable 151 canalso be hauled in by the second marine system 150 to get to pipeline131.

The invention claimed is:
 1. A marine pipeline installation system forlaying an offshore pipeline, wherein the system comprises: a vessel, apipeline launch tower comprising pipe laying equipment defining a towerfiring line, which tower is mounted pivotably about a tower pivot axison said vessel and which is adapted for launching the pipeline in thetower firing line into the sea in a first position of the tower in whichthe tower is at an angle α with respect to the vertical, an abandonmentand recovery (A&R) system comprising at least one A&R cable and a sheavearrangement with a plurality of sheaves supported by the pipeline launchtower, a hang off module supported in the lower part of the tower firingline for clamping and supporting the weight of previously launchedpipeline, wherein two of the plurality of sheaves used to guide the atleast one A&R cable having a sheave pivot axis substantially parallel tothe tower pivot axis are supported by a support frame, the support frameis skiddable along a support frame guide provided in a lower part of thepipeline launch tower, the support frame guide is provided substantiallyperpendicular to the tower pivot axis and substantially perpendicular tothe tower firing line, such that the two of the plurality of sheavessupported by the support frame are skiddable into and out of the towerfiring line, and wherein the two of the plurality of sheaves aresupported by the support frame through respective mechanisms, allowing amovement with respect to the tower pivot axis between a one cable guideposition and a double fall A&R position.
 2. The marine pipelineinstallation system according to claim 1, wherein at least one of thesheaves supported by the support frame is adapted to guide the at leastone A&R cable at opposite sides of the sheave, and the support frame isat least skiddable between a position in which the at least one A&Rcable is guided by a first side of the sheave and another position inwhich the at least one A&R cable is guided by an opposite side of thesheave.
 3. The marine pipeline installation system according to claim 1,further comprising cylinders provided between the two of the pluralityof sheaves and the support frame, wherein actuation of the cylindersenables a movement of the sheaves with respect to the tower pivot axis.4. The marine pipeline installation system according to claim 1, whereinthe movable sheaves enable the A&R system to be adjustable from a singlefall system in which a moveable sheave is positioned adjacent a singleA&R cable to guide this single A&R cable, to a double fall system inwhich the two of the plurality of sheaves are positioned adjacent twoA&R cables to guide these two A&R cables.
 5. The marine pipelineinstallation system according to claim 1, wherein the hang off module issupported by the support frame as well.
 6. A marine pipelineinstallation system for laying an offshore pipeline, wherein the systemcomprises: a vessel, a pipeline launch tower comprising pipe layingequipment defining a tower firing line, which tower is mounted pivotablyabout a tower pivot axis on said vessel and which is adapted forlaunching the pipeline in the tower firing line into the sea in a firstposition of the tower in which the tower is at an angle α with respectto the vertical, an abandonment and recovery (A&R) system comprising atleast one A&R cable and a sheave arrangement with one or more sheavessupported by the pipeline launch tower, a hang off module supported inthe lower part of the tower firing line for clamping and supporting theweight of previously launched pipeline, wherein the hang off module andone or more of the sheaves having a sheave pivot axis substantiallyparallel to the tower pivot axis are supported by a support frame, thesupport frame is skiddable along a support frame guide provided in alower part of the pipeline launch tower, and the support frame guide isprovided substantially perpendicular to the tower pivot axis andsubstantially perpendicular to the tower firing line, such that the oneor more sheaves and the hang off module supported by the support frameare skiddable into and out of the tower firing line.
 7. The marinepipeline installation system according to claim 6, wherein at least oneof the sheaves supported by the support frame is adapted to guide the atleast one A&R cable at opposite sides of the sheave, and the supportframe is at least skiddable between a position in which the at least oneA&R cable is guided by a first side of the sheave and another positionin which the at least one A&R cable is guided by an opposite side of thesheave.
 8. The marine pipeline installation system according to claim 6,wherein at least one of the sheaves supported by the support frame ismovable in a direction substantially parallel to the tower pivot axis.9. The marine pipeline installation system according to claim 6, whereintwo sheaves are supported by the support frame, at least one of which ismoveable in a direction substantially parallel to the tower pivot axis,such that the A&R system is adjustable from a single fall system inwhich the moveable sheave is positioned adjacent a single A&R cable toguide this single A&R cable, to a double fall system in which the twosheaves are positioned adjacent two A&R cables to guide these two A&Rcables.
 10. The marine pipeline installation system according to claim6, wherein the support frame further supports a working platformaccessible to personnel to perform inspection operations etc., such thatthe working platform is also skiddable into and out of the tower firingline.
 11. The marine pipeline installation system according to claim 10,wherein between the support frame and the working platform a platformpivot axis parallel to the tower pivot axis is provided, such that theworking platform can gimbal maintaining a horizontal positionindependent of the position of the tower.
 12. The marine pipelineinstallation system according to claim 11, wherein a platform portionpositioned closest to the tower firing line extends over the one or moresheaves supported by the support frame, and wherein the working platformcomprises two platform portions, between which a swinging axis parallelto the tower pivot axis is provided, such that the platform portionclosest to the tower firing line can be swung back so as to reveal theone or more sheaves.
 13. The marine pipeline installation systemaccording to claim 12, in which the swinging axis coincides with theplatform pivot axis.